#include <bits/stdc++.h>
#include <queue>

using namespace std;
using ll = long long;

const int MAXN = 100'001;

vector<pair<int, ll>> g[MAXN];
vector<int> g2[MAXN];
int dp[MAXN], n, m, a, b;
ll dist[MAXN];

void dijkstra(int source) {
	fill(dist, dist+MAXN, 1e18);
	priority_queue<pair<ll, int>, vector<pair<ll, int>>, greater<pair<ll, int>>> pq;
	dist[source] = 0;
	pq.push({0, source});
	while (!pq.empty()) {
		auto [d, u] = pq.top(); pq.pop();
		if (dist[u] != d) continue;
		for (auto [v, w] : g[u]) {
			if (dist[v] > dist[u] + w) {
				dist[v] = dist[u] + w;
				pq.push({dist[v], v});
			}
		}
	}
}

void build_graph() {
	for (int i = 1; i <= n; i++) {
		for (auto [u, w] : g[i]) {
			if (dist[i] >= dist[u]) {
				g2[i].emplace_back(u);
			}
		}
	}
}

int longest_route(int u) {
	if (dp[u] == -1) {
		dp[u] = INT_MIN;
		for (int v : g2[u]) {
			dp[u] = max(dp[u], 1 + longest_route(v));
		}
	}
	return dp[u];
}

int main() {
	ios::sync_with_stdio(0); cin.tie(0);
	fill(dp, dp+MAXN, -1);
	cin >> n >> m >> a >> b;
	for (int i = 0; i < m; i++) {
		int u, v; ll w; cin >> u >> v >> w;
		g[u].emplace_back(v, w);
		g[v].emplace_back(u, w);
	}
	dp[b] = 0;
	dijkstra(b);
	build_graph();
	cout << longest_route(a) << "\n";
	int u = a;
	while (u != b) {
		pair<int, int> best = {-1, 0};
		dp[u] = INT_MIN;
		cout << u << " ";
		for (int v : g2[u]) {
			best = max(best, {dp[v], v});
		}
		u = best.second;
	}
	cout << b << "\n";
	return 0;
}